This invention relates to dc-to-dc converters, and more particularly to multiphase converters with two-loop feedback control.
In a single-phase dc-to-dc converter, a signal x which indicates the state of the single power switch is the principal determinant of switching instants for two-loop feedback control. One feedback loop is for that pulsed signal and the other is for the output voltage e.sub.o. The two are added, compared with a reference and the difference, a pulsed error signal X, is applied to an integrator where the rectangular pulse waveform is converted to a sawtooth waveform. A comparator or threshold detector determines when the sawtooth waveform attains a predetermined (zero or non-zero) level. Each time that level is reached, a pulse generator is triggered to turn the power switch on for a fixed time, T. If the output voltage e.sub.o increases, the minimum level is reached later, thus delaying the time for the power switch to be turned on again. Conversely, if the output voltage e.sub.o decreases the minimum level is reached earlier, thus advancing the time for the power switch to be turned on again. The pulsed power delivered by the switch is filtered to provide the dc output voltage e.sub.o.
Since all of the power delivered to the load must be provided through the single power switch, a dc-to-dc converter with two-loop control is limited in load capacity. For greater load capacity, it would be desirable to provide additional power switches in parallel, but the problem would then be to design a circuit that assures equal division of the load. That problem can be avoided by operating the power switches in phase-staggered sequence, but since one of the two feedback loops indicates the state of the power switch as the principal determinant of switching instants, two-loop control of N phase-staggered power switches implicitly requires 2N feedback loops, two loops for each of the N power switches, and a synchronizing circuit to maintain proper phase relationship. Consequently, a multiphase dc-to-dc converter with two-loop control would, but for the present invention, entail greatly increased complexity and component count.